B12 level for hypothyroidism

[SNEWEY]

Some time ago I read that for people with hypothyroidism, B12 readings needed to be a lot higher eg 1000. Can't find where I read it. Can anyone pont me in the right direction please? Thank you

[Foggyme Administrator]

Hi Snewey.

You might be better asking this question on the thyroid forum since they have more experience on how B12 levels impact on thyroid function.

In this forum, we would say that following treatment with B12 supplements (injections or otherwise) what counts is whether you are symptomatic or not, not what the serum B12 levels are (though these would be high (perhaps over the top of the reference range) following injections.

👍

[Gambit62 Administrator]

To follow on from Foggyme 's reply.

There does seem to be quite a bit on TUK about needing really high levels of B12 if you are hypothyroid.

Reality is that the serum B12 test is a poor guide to whether you have B12 levels that are right for you - as a single measure it will miss 25% who are B12 deficient but also pick up 5% who are - so symptoms are always important in evaluating a potential deficiency. Macrocytosis is one common symptom that won't overlap with thyroid but that isn't present in 25% of people presenting with B12 deficiency so if your thyroid isn't under control that can make evaluating a B12 deficiency very difficult.

After loading shots normal range really doesn't seem to apply - and this is probably where the 1000 (ng/L?) comes from - as this has been found in some studies to be the average level that people who have been treated for B12 deficiency find they need to maintain their B12 levels at ...

If your thyroid problem is auto-immune then there is a higher chance of having another auto-immune condition, like B12 deficiency.

Serum B12 certainly isn't a test that you can use to evaluate whether your levels are adequate and on that basis I'd have to say that 'need levels of 1000' is rather unsound logic. Certainly not aware of any scientific evidence or studies that have said that people with any thyroid problems need B12 levels higher than other people, unless they also have and are being treated for a B12 absorption problem.

Further,supplementing with high dose B12 can also cause problems - possibly down to functional deficiency caused by raising blood serum levels over the normal range - that could trap you in forever needing to keep B12 levels much higher than you would otherwise have needed them to be.